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I think there is a big difference in risk between kendo vs. kenjutsu/koryu/iaido. There is a definite risk of being knocked over and falling in kendo, since there is sparring involved. Kenjutsu, koryu, and iaido has little to no sparring that I am aware of and thus you don't have that risk. (I'm not an expert in those fields though. Others may have better idea) There should be no intentional hits to the back. At most a push on your butt in kendo to keep you moving.

Are you in England or Turkey? There are definitely reputable dojos in England. There are many people on this forum that practice there that can advise you where to go.